1. Field of the Invention
This invention relates to inhibitors for double-base propellants.
2. Description of the Prior Art
Nitroglycerine is a major ingredient of all double-base propellants. When double-base propellants are stored for any length of time, nitroglycerine tends to migrate to the surface. Inhibitor layers are applied to the surface of double-base propellant grains in order to provide controlled burning surface area for designed ballistic performance. The nitroglycerine migrates into this inhibitor, depleting the propellant and affecting its ballistic properties. The properties of the inhibitor also deteriorate physically as more and more nitroglycerine plasticizes the material.
Over the past 25 or 30 years, a great deal of money and effort has been expended in attempts to find ways in which suitable inhibitor materials, i.e., materials which are impervious to nitroglycerine, could be adhered to double-base propellant grains. This has proven to be a difficult problem. Many materials have been tried but most of those which could be bound, by means of adhesive, to a double-base propellant grain have proven either to be pervious to unacceptably large amounts of nitroglycerine or, in many cases, the adhesive itself took up nitroglycerine and softened, resulting in low cohesive strength. The latter is a dangerous situation for when the pressure increases due to propellant ignition the weak adhesive layer can part from the propellant surface. If this happens a large increase in burning area, beyond the design of the rocket, is provided. The usual result is a rocket motor blowup.
At the present time, ethyl cellulose and various cellulose acetates are most widely used as inhibitor materials. Ethyl cellulose picks up from 15 to 30 percent nitroglycerine, high acetyl cellulose acetate dissolves in nitroglycerine and medium or low acetyl cellulose acetate picks up high percentages of nitroglycerine.